The Missouri River is nicknamed the "Big Muddy". But for the last 50 years that description applies more to its politics than the water. Ever since a half dozen dams were built on the upper Missouri, most of the river is surprisingly clear. But the dam's clouded the river's politics like never before. The fallout has divided the Missouri basin into two camps: upstream and downstream. And so far downstream is winning. Mark Steil begins a new Mainstreet Radio series we call, "Water Wars." HOST BACKANNOUNCE: This year the Garrision Dam, on the upper Missouri, is 50 years old. Our series continues on All Things Considered with a look back at that project and the bitterness that still exists. There's much more on the web at Minnesota Public Radio dot-org.